Adrenal chromaffin, cells from different mammalian species contain gamma-aminobutyric acid, glutamic acid decarboxylase, GABA aminotransferase, and GABA receptors. GABA and glutamic acid decarboxylase are also present in fibers impinging upon adrenal chromaffin cells. The membranes of chromaffin cells contain GABA/Benzodiazepine binding sites linked to Cl-channels. Occupation of these receptors with GABA or GABA mimetics appears to modulate the acetyldoline-induced release of catecholamines and enkephalin-like peptides in parallel direction.